You find the area of the circle by using A = πr^2. Next you find the area of the square by finding the circle diameter since the circle touches side to side, and then multiply the diameter (width of square) x diameter (height of square) = the area of the square. From there just subtract the area of the square by the area of the circle = the none over lapping area of the square. You needed to subtract the area of the square by the area of the circle because the none over lapping are of the square is those little triangles on the corners.
Hope this helps :)